The present invention relates to an imprint manufacture method and apparatus, a magnetic recording medium, and its manufacture apparatus.
The fine patterning technology for semiconductor manufacture has developed remarkably. The currently required and available critical dimension processing accuracy is 100 nm or smaller. Fine patterning technologies onto resist on a silicon wafer have used photolithography, direct imaging using an electron beam, and the like. Photolithography has improved the resolution with a shortened wavelength of a light source, but the exposure apparatuses are very expensive and transferring a pattern of 100 nm or smaller is difficult. On the other hand, the direct imaging using an electron beam has superior resolution but poor mass-productivity.
The nanoimprint lithography (“NIL”) has been proposed (see U.S. Pat. No. 5,772,905) as a solution for the problem of poor mass-production technology of fine patterned devices. The NIL presses a mold having a nano-scale fine structure against the resist on a silicon wafer, and transfers the fine pattern onto the resist.
A description will be given of a NIL process with reference to FIGS. 9A-9E. A mold 3 uses, for example, a silicon thermal-oxide film patterned with electron-beam direct imaging, etc. First, as shown in FIG. 9A, a thin film 5 is formed as a resist with poly (methyl methacrylate) (“PMMA”) as thermoplastic resin etc. on a silicon wafer 4. Next, as shown in FIG. 9B, the mold 3 held by a mold support 20 is pressed against the resist 5, and a fine pattern on the mold 3 is transferred onto the resist 5. The resist 5 is subject to compressive transferring while heated above the glass transition temperature (Tg) and softened. After the transfer completes, it is cooled and hardened, and the mold 3 is peeled off from the resist 5. Next, as shown in FIG. 9C, oxygen etching 21, etc. removes the remaining film to expose a silicon surface, as shown in FIG. 9D. As shown in FIG. 9E, after etching removes the resist, it is used as a single silicon device.
This manufacture method can transfer a pattern of 10 nm or smaller and has attracted attentions as the next generation for fine processing, only if the mold is available through time-consuming processing, fine patterns can be mass-produced using a more cost-efficient apparatus than a conventional processing machine.
In order to soften the resist and improve the transfer rate, some imprint methods have been proposed including one that uses supercritical fluid (see Japanese Patent Application Publication No. 2002-270540) and one that transfers a pattern under low pressure at room temperature (see Japanese Patent Application Publication No. 2002-184718).
Magnetic recording media called patterned media have been proposed recently (see Japanese Patent No. 1,888,363). Japanese Patent No. 1,888,363 discloses a base structure of the patterned media that arranges ferromagnetic particulates along a track at regular intervals, and records every bit on each ferromagnetic particulate. An application of the patterned media has been also proposed (see, for example, Japanese Patent Application Publication No. 2001-110050). A description will be given of the manufacture flows with reference to FIGS. 10A-10F and FIGS. 11A-11F.
First, as shown in FIG. 10A, a sputtering process arranges an amorphous carbon matrix thin film 5600 between a substrate 1000 and a resist 2000. Then, as shown in FIG. 10B, the electron-beam images the resist 2000, and a reactive ion etching (“RIE”) process using fluoro-carbons and the resist as a mask, patterns amorphous carbon matrix thin film 5600, as shown in FIG. 10C. As shown in FIG. 10D, a magnetic layer 5700 is made by a sputtering process, and subjected to a lift-off process that dissolves and removes the resist mask 2000, as shown in FIG. 10E. As shown in FIG. 10F, a sputtering process forms a lubricating layer 5800 as an amorphous carbon layer, as shown in FIG. 10F.
A description will now be given of the manufacturing process disclosed in Japanese Patent Application Publication No. 2001-110050 with reference to FIGS. 11A-11F. First, resist 2000 is formed on a glass substrate 1000, as shown in FIG. 11A. As shown in FIG. 11B, electron-beam exposure and development follows. RIE then forms the mask pattern 2000 as shown in FIG. 11C. As shown in FIG. 11D, the magnetic thin film 5700 is made by a sputtering process, followed by the lift-off as shown in FIG. 11E. The surface lubricating layer 5800 is formed to form a patterned media, as shown in FIG. 11F.
However, the manufacture method disclosed in U.S. Pat. No. 5,772,905 needs to heat the resist above Tg and press at a high pressure. For example, the experiment conducted by inventors of U.S. Pat. No. 5,772,905 heated the resist with Tg of 105° C., up to 200° C. or higher, and applied a pressure of 13 MPa. An example report states that the applied pressure of 87 MPa at 170° C. is required to transfer a convex pattern with a critical dimension of 2 μm and a height of 340 nm onto PMMA resist. These conventional methods require an application of high pressure, and disadvantageously destroy the mold and the pattern on it.
A high strength diamond or SiC mold has been proposed as one solution for the above problem. However, the manufacture of such molds becomes disadvantageously expensive.
The conventional NIL method has had difficulties in alignment between a mold and a silicon wafer since the mold does not transmit light. Therefore, this method has been inapplicable for semiconductor manufacture processing due to poor pattern alignment when forming multiple layers. A mold made of a transparent material, such as quartz, would be easily destroyed and be unfeasible.
Conventional semiconductor manufacture processing also leaves fine defects, mainly in organic material(s) on minutely patterned resist, requiring cleansing of the resist surface. Use of an organic solvent, such as a rinse, for cleansing fluid in this cleansing step would disadvantageously destroy a pattern on the resist due to the surface tension at the interface between the gas and liquid phases. The above problem has become serious as the pattern becomes finer and the aspect ratio becomes higher.
Also disadvantageous is a high temperature of a wafer substrate at the time of pressing. This weakens the adhesion between the resist and the substrate, cause partial stripping of a polymer membrane after pressing, and cause difficulties in forming a large-scale fine pattern. Cooling of the substrate temperature below Tg of the resist when peeling off the resist from the mold would disadvantageously lower the throughput.
Japanese Patent Application Publication No. 2002-270540 presses a mold against a resist that contains softener for transferring in a chamber that receives supercritical fluid. This method hardens the resist by extracting the softener in the resist with supercritical fluid. Maintenance of pressing is required until the extraction is completed. In order to extract the softener, the supercritical fluid should infiltrate through a minute aperture corresponding to the resist's thickness between the mold and substrate. Therefore, because it takes time to infiltrate into the resist, a large-scale pattern was hard to be mass-produced.
Japanese Patent Application Publication No. 2002-184718 selects chemical amplification resist, holds acid chemicals on convex portions on the mold, and provides a heat treatment to the substrate after pressing it, thereby causing the resist to exhibit an insolubilization or solubilization reaction only at acid filtrated portions. Thereafter, the development of the resist forms convex and concave patterns corresponding to the mold pattern. However, it is anticipated that this method has difficulty in selectively infiltrating acid only into the convex portions on large-scale mold patterns. In particular, it is difficult to infiltrate chemicals only into the convex pattern portions and to accurately form fine patterns, such as those below 200 nm.
A method disclosed in Japanese Patent Application Publication No. 2001-110050 can increase the capacity of a magnetic disc, but the electron-beam imaging causes low throughput. A mass-productive imprinting manufacture method has been proposed (for example, in Japanese Patent Application Publication No. 2003-157520) which provides a process for manufacturing patterned media, and efficiently equalizes press pressure by arranging a buffer layer that has an area corresponding to a recording area and narrower than a substrate and a mold area, between the upper and lower pressing surfaces and one of the mold pattern and the substrate. An application of press pressure above 500 bars would form a pattern at a temperature below the glass transition temperature of the resist, and achieve high throughput. This method, however, has a problem because high press pressure damages the mold and the substrate. Therefore, one mold cannot manufacture many patterned media.